Semiconductor memory

ABSTRACT

Manufacturing processes for phase change memory have suffered from the problem of chalcogenide material being susceptible to delamination, since this material exhibits low adhesion to high melting point metals and silicon oxide films. Furthermore, chalcogenide material has low thermal stability and hence tends to sublime during the manufacturing process of phase change memory. According to the present invention, conductive or insulative adhesive layers are formed over and under the chalcogenide material layer to enhance its delamination strength. Further, a protective film made up of a nitride film is formed on the sidewalls of the chalcogenide material layer to prevent sublimation of the chalcogenide material layer.

TECHNICAL FIELD

The present invention relates to a technique that is effective whenapplied to semiconductor integrated circuit devices which employ phasechange memory cells formed of a phase change material such aschalcogenide.

BACKGROUND ART

Mobile devices, typified by cellular phones, use a semiconductor memorysuch as a DRAM, SRAM, or flash memory. A DRAM provides large capacitybut its access speed is low. A SRAM, on the other hand, is high-speedmemory, but is not suitable for forming a large capacity memory, sinceeach cell requires a number of transistors (4 to 6 transistors) andhence it is difficult to produce highly integrated SRAM. DRAM and SRAMmust continuously receive power to retain data; that is, they arevolatile memories. Flash memory, on the other hand, is a nonvolatilememory; it does not need to continuously receive power to electricallyretain data. However, the flash memory is disadvantageous in that itsprogram/erase count is limited to a maximum of approximately 10⁵ and itsreprogramming speed is a few orders of magnitude lower than those ofother memories. Since each memory (described above) has itsdisadvantage, it is current practice to select suitable memory dependingon the application.

If a universal memory having all the advantages of DRAM, SRAM, and flashmemory were developed, a plurality of memories could be integrated on asingle chip, which allows cellular phones and other mobile devices to beminiaturized and enhanced in functionality. If the universal memorycould replace all other types of memory, it would have a tremendousimpact (on the semiconductor industry). The requirements for universalmemory are that: (1) like DRAM, it is highly integrated (and hence canhave large capacity); (2) its access (write/read) speed is high,comparable to that of SRAM; (3) it has the same nonvolatility as flashmemory; and (4) it exhibits low power consumption and hence can bepowered by a small battery.

Among next-generation nonvolatile memories referred to as universalmemories, phase change memory is currently attracting the mostattention. Phase change memory uses a chalcogenide material, which isalso used by CD-RWs and DVDs. Like these disks, phase change memorystores data by assuming two states: a crystalline state and an amorphousstate. However, they differ in how data is written to or read from them.Specifically, whereas a laser is used to write to or read from CD-RWsand DVDs, the Joule heat generated by an electrical current is used towrite data to the phase change memory and the change in the resistanceof the memory due to the phase change is read as a data value.

The principle of operation of phase change memory will be described withreference to FIG. 2. When a chalcogenide material is amorphized, such areset pulse is applied that causes the chalcogenide material to berapidly quenched after it is heated to a melting point or more. Themelting point is, for example, 600° C., and the quench time (t1) is, forexample, 2 nsec. When crystallizing the chalcogenide material, on theother hand, a set pulse is applied to the memory so as to maintain thechalcogenide material at a temperature between its crystallization pointand melting point. The crystallization point is, for example, 400° C.,and the time (t2) required for the crystallization is, for example, 50nsec.

A feature of phase change memory is that the resistance value of thechalcogenide material (of the phase change memory) varies by two tothree orders of magnitude depending on its crystallization state. Since(the change in) the resistance value is used as a signal, the readsignal is large, facilitating the sense operation and hence increasingthe speed of the read operation. Another feature of the phase changememory is that it can be reprogrammed 10¹² times, which is an advantageover flash memory. Still another feature of the phase change memory isthat it can operate at a low voltage and low power, which allows it tobe formed on the same chip as logic circuitry. Therefore, phase changememory is suitable for use in mobile devices.

An exemplary manufacturing process for a phase change memory cell willnow be briefly described with reference to FIGS. 3 to 5. First, a selecttransistor is formed on a semiconductor substrate by a knownmanufacturing method (not shown). The select transistor is made up of aMOS transistor or bipolar transistor. Then, an interlayer insulatingfilm 1 made up of a silicon oxide film is deposited and a plug 2 of, forexample, tungsten is formed in the interlayer insulating film 1 by aknown manufacturing method. This plug is used to electrically connectbetween the select transistor and the phase change material layeroverlying the select transistor. Then, a chalcogenide material layer 3of, for example, GeSbTe, an upper electrode 4 of, for example, tungsten,and a hard mask 5 made up of, for example, a silicon oxide film aresequentially deposited, forming the structure shown in FIG. 3.

Then, the hard mask 5, the upper electrode 4, and the chalcogenidematerial layer 3 are processed by a known lithographic technique and dryetching technique, as shown in FIG. 4.

After that, an interlayer insulating film 6 is deposited, as shown inFIG. 5.Then, a wiring layer electrically connected to the upper electrode 4 isformed on the interlayer insulating film 6, and a plurality of otherwiring layers are formed on the wiring layer on the interlayerinsulating film 6, completing formation of phase change memory (notshown).

Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-174144Patent Document 2: Japanese Laid-Open Patent Publication No. 2003-229537DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

There are two problems that make it difficult to manufacture phasechange memory: the low adhesive strength and the low thermal stabilityof the chalcogenide material. How the manufacturing process is affectedby each problem will be specifically described.

First, since chalcogenide material has low adhesive strength, it tendsto delaminate (or peel) during the manufacturing process. Since thechalcogenide material is heated to its melting point or a highertemperature when the phase change memory is in operation (as describedabove), the plug and the upper electrode in contact with thechalcogenide material must be formed of a high melting point metal. Forexample, tungsten is a high melting point metal conventionally used insemiconductor integrated circuit devices. However, we have found thatsince chalcogenide material (layer) has low adhesion to high meltingpoint metals such as tungsten, it tends to delaminate at its interfaceswith the plug and the upper electrode. Furthermore, since thechalcogenide material also exhibits low adhesion to silicon oxide films,it also tends to delaminate at its interface with the interlayerinsulating film.

It is obvious that the manufacturing process described with reference toFIGS. 3 to 5 produces a phase change memory cell in which thechalcogenide material exhibits low adhesion at its upper and lowerinterfaces. Therefore, there is a need for a means of enhancing theadhesive strength of the chalcogenide material (at these interfaces).

Second, since the thermal stability of chalcogenide material is low, ittends to sublime during the manufacturing process. FIGS. 6A to 6C showresults of thermal desorption spectrometry of a GeSbTe film. Thisanalysis was conducted in ultrahigh vacuum (approximately, 10⁻⁷ Pa).When the GeSbTe film was heated to approximately 300° C., the elementsGe, Sb, and Te sublimed at the same time, as shown in the figures. Thesample was further heated to 500° C. and then cooled to roomtemperature. After this, we retrieved the sample and found that theGeSbTe film had completely disappeared. Thus, chalcogenide material hasvery low thermal stability. The low thermal stability of thechalcogenide material does not cause problems with CD-RW and DVDmanufacturing processes, since these processes do not include anyhigh-temperature heating process. (That is why CD-RWs and DVDs employ asubstrate of polycarbonate, which has low heat resistance.) However,care must be taken when using a chalcogenide material in a semiconductorintegrated circuit device whose manufacture includes a wiring process inwhich the wafer is heated to 400° C. or higher. FIG. 7 is a graphshowing the sublimation characteristics of a GeSbTe film, wherein thehorizontal axis represents temperature and the vertical axis representspressure. Specifically, the temperature and pressure at which the GeSbTefilm was heat-treated were varied. In the figure, each open circleindicates a condition in which the GeSbTe film did not sublime, whileeach solid circle indicates a condition in which the GeSbTe filmsublimed. As show in the figure, the lower the pressure under which theGeSbTe film was heat-treated, the lower the temperature at which itsublimed. A manufacturing process of a semiconductor integrated circuitdevice performs, for example, chemical vapor phase growth at a pressureof approximately 10⁻¹-10 ³ Pa and a temperature of approximately400-700° C.

As can be seen from FIG. 7, the GeSbTe film will sublime if it isdirectly exposed to these conditions.In the manufacturing process described with reference to FIGS. 3 to 5,the interlayer insulating film 6 must be formed by chemical vapor phasegrowth, which is superior in terms of step coverage. As a result, thechalcogenide material layer 3 might sublime at its sidewalls. Therefore,there is a need for a means for maintaining the thermal stability ofchalcogenide material even if a portion of the material is exposed.

Means for Solving the Problems

The above objects may be achieved by a semiconductor memory devicecomprising: a semiconductor substrate; a select transistor formed on aprincipal surface of the semiconductor substrate; an interlayerinsulating film provided on the select transistor; a plug provided so asto penetrate through the interlayer insulating film, and electricallyconnected to the select transistor; a phase change material layerprovided so as to extend over the interlayer insulating film, andconnected with the plug; an upper electrode provided on the phase changematerial layer; and an adhesive layer provided between an under surfaceof the phase change material layer and top surfaces of the interlayerinsulating film and the plug.

Further, the above objects may also be achieved by a semiconductormemory device comprising: a semiconductor substrate; a select transistorformed on a principal surface of the semiconductor substrate; aninterlayer insulating film provided on the select transistor; a plugprovided so as to penetrate through the interlayer insulating film, theplug being electrically connected to the select transistor; a phasechange material layer provided on the interlayer insulating film suchthat a portion of the phase change material layer is connected with theplug; an upper electrode provided on the phase change material layer;and a protective film formed on at least a sidewall of the phase changematerial layer and containing a silicon nitride.

Effects of the Invention

The major effects of the present invention will now be brieflydescribed.

The adhesive layers formed over and under the chalcogenide materiallayer can prevent delamination of the chalcogenide material layer duringthe manufacturing process. Further, the protective film formed on thesidewalls of the chalcogenide material layer can prevent sublimation ofthe chalcogenide material layer during the manufacturing process.These arrangements improve the phase change memory manufacturing processin such a way as to reduce variations in the electrical characteristicsof the phase change memory, as well as preventing reliabilitydegradation.

BEST MODES FOR CARRYING OUT THE INVENTION

A first means of the present invention is to form adhesive layers overand under the chalcogenide material (layer) so as to enhance theadhesive strength of the chalcogenide material (at its interfaces withthe overlying and underlying layers).

First, the effects of these adhesive layers will be described. We formedGeSbTe films on SiO₂ films to a thickness of 100 nm, and performed ascratch test on these GeSbTe films to compare their delaminationstrength. In a scratch test, a thin film surface of a sample isscratched by an indenter while applying a load to the sample in thevertical direction, in order to determine the minimum load that causedelamination (referred to as the “critical delamination load”). Thehigher the critical delamination load, the higher the delaminationstrength. FIG. 8 shows the (critical delamination load) measurementresults. As shown in FIG. 8, the delamination strength of the GeSbTefilm was extremely low when an adhesive layer was not inserted (betweenthe GeSbTe film and the SiO₂ film). Further, insertion of a W layer didnot lead to any improvement in the delamination strength of the GeSbTefilm. This reflects the fact that chalcogenide material has low adhesionto high melting point metals. On the other hand, inserting an Almaterial layer increased the delamination strength of the GeSbTe film bya factor of 7-9, and inserting a Ti material layer enhanced thedelamination strength by a factor of 10-15.

These results indicate that insertion of an adhesive layer may beeffective in enhancing the adhesive properties of the chalcogenidematerial. As can be seen from FIG. 8, Ti material is superior to Almaterial as an adhesive layer. Further, nitrides have higher adhesion tochalcogenide material than oxides, and individual metals have higheradhesion than oxides and nitrides.

An exemplary manufacturing process of the present invention will bedescribed with reference to FIG. 1. First, an interlayer insulating film1 and a plug 2 are formed by a conventional technique. Then, thefollowing layers are sequentially deposited: an adhesive layer 7 of, forexample, titanium; a chalcogenide material layer 3 of, for example,GeSbTe; an adhesive layer 8 of, for example, titanium; an upperelectrode 4 of, for example, tungsten; and a hard mask 5 made up of, forexample, a silicon oxide film. Then, the hard mask 5, the upperelectrode 4, the adhesive layer 8, the chalcogenide material layer 3,and the adhesive layer 7 are processed by a known lithographic techniqueand dry etching technique, forming the structure shown in FIG. 1.

Thus, in the above manufacturing process, adhesive layers are formedover and under the chalcogenide material layer, which increases thedelamination strength of the chalcogenide material layer and therebyprevents its delamination during the manufacturing process.

It should be noted that although in the above example two adhesivelayers are formed over and under, respectively, the chalcogenide layer,the present invention is not limited to this particular arrangement. Anadhesive layer may be formed only either over or under the chalcogenidelayer.

The desired thickness of the adhesive layers will now be described.FIGS. 9A and 9B show the temperature vs. resistance characteristics ofGeSbTe films. Specifically, FIG. 9A shows the temperature vs. resistancecharacteristics of a GeSbTe film with no adhesive layer. When the GeSbTefilm set in an amorphous state was heated, it crystallized atapproximately 120-130° C. and, as a result, its resistance rapidlydecreased. Then, the film was cooled after being heated to approximately200° C. (as shown in FIG. 9A). The resistance of the GeSbTe film changedby five or more orders of magnitude (between the amorphous andcrystalline states). Since phase change memory uses the resistance valueof the chalcogenide material layer as a signal, the larger the change inthe resistance of the chalcogenide material between amorphous andcrystalline states, the better. On the other hand, FIG. 9B shows thetemperature vs. resistance characteristics of a GeSbTe film with a 2.5nm thick adhesive layer of titanium. In this case, the GeSbTe film hadlow resistance even when it was in an amorphous state. The GeSbTe filmwas heated to approximately 200° C., so that the film crystallized.Then, the GeSbTe film was cooled. The resistance did not change much(between the amorphous and crystalline states). The reason for this maybe that titanium within the adhesive layer diffused into the GeSbTefilm. This indicates that if the adhesive layer has a small thickness,it may degrade the characteristics of the phase change memory.

The thickness of the adhesive layers in phase change memory ispreferably 5 nm or less although this may vary depending on the materialof these layers. Further, the thickness of the adhesive layers is morepreferably 2 nm or less to increase the ratio between the resistancevalues in amorphous and crystalline states.

The desired materials for the adhesive layers will now be described. Acurrent (as a set pulse or reset pulse) is supplied from the selecttransistor to the chalcogenide material (layer) through the plug tochange the phase of the chalcogenide material. To efficiently deliverthis current to the chalcogenide material, the adhesive layer at theinterface between the chalcogenide material layer and the plug ispreferably electrically conductive. Likewise, the adhesive layer at theinterface between the chalcogenide material layer and the upperelectrode is also preferably conductive.

Further, the smaller the regions used to change the phase of thechalcogenide material, the smaller the current required forreprogramming (the memory cell). That is, to reduce the powerconsumption of the phase change memory cell, all regions other than theplug need be insulative (or nonconductive), and the adhesive layer atthe interface between the chalcogenide material layer and the interlayerinsulating film is preferably insulative.

FIG. 10 shows a phase change memory cell using an ideal material for theadhesive layers. Referring to the figure, a conductive adhesive layer 9is formed at the interface between a chalcogenide material layer 3 and aplug 2; an insulative adhesive layer 10 is formed at the interfacebetween the chalcogenide material layer 3 and an interlayer insulatingfilm 1; and a conductive adhesive layer 11 is formed between thechalcogenide material layer 3 and an upper electrode 4.

Examples of conductive adhesive layers include Ti, Al, Ta, Si, Tinitride, Al nitride, Ta nitride, W nitride, TiSi, TaSi, WSi, TiW, TiAlnitride. TaSi nitride, TiSi nitride, and WSi nitride films. Further,since Te in chalcogenide material is reactive with Ti and Al, a layerformed of a compound of Ti and Te, or Al and Te, may be used as aconductive adhesive layer. Examples of insulative adhesive layersinclude Ti oxide, Al oxide, Ta oxide, Nb oxide, V oxide, Cr oxide, Woxide, Zr oxide, Hf oxide, and Si nitride films.

Further, the adhesive layer at the interface between the chalcogenidematerial layer and the interlayer insulating film need not necessarilybe insulative (or nonconductive) if the chalcogenide material layer isnot (fully) electrically connected to the interlayer insulating film.(This also reduces the regions used to cause a change in the phase ofthe chalcogenide material.) For example, the adhesive layer may be aconductive layer having an island shape (i.e., a discontinuousconductive layer). In this case, the adhesive layer at the interfacebetween the chalcogenide material layer and the plug and the adhesivelayer at the interface between the chalcogenide material layer and theinterlayer insulating film can be formed of the same material at thesame time. When an adhesive layer is formed to an island shape (or whena discontinuous adhesive layer is formed), its thickness is preferably 2nm or less. Further, the thickness of the adhesive layer is morepreferably 1 nm or less to increase or ensure the electricaldiscontinuity (between the chalcogenide material layer and theinterlayer insulating film). For example, the adhesive layers may beformed of titanium to a thickness of 0.5 nm.

It should be noted that Patent Document 1 (listed above), for example,discloses means for using an adhesive layer to improve the adhesionbetween a chalcogenide material and a dielectric material. The presentinvention is different from this technique. As described above, in aphase change memory cell, the plug and the upper electrode must beformed of a high melting point metal such as tungsten. However, we havefound that the chalcogenide material tends to delaminate at itsinterfaces with such a plug and upper electrode. The present inventionhas been devised to solve this problem. On the other hand, the aboveknown technique (disclosed in Patent Document 1) is intended to insertan adhesive layer only between a chalcogenide material and an interlayerinsulating film (formed of a dielectric material), which is distinctlydifferent from the technique of the present invention.

A second means of the present invention is to form a protective film onthe sidewalls of the chalcogenide material layer to ensure the thermalstability of the chalcogenide material.

An exemplary manufacturing process of the present invention will bedescribed with reference to FIG. 11. First, an interlayer insulatingfilm 1 and a plug 2 are formed by a conventional technique. Then, achalcogenide material layer 3 of, for example, GeSbTe, an upperelectrode 4 of, for example, tungsten, and a hard mask 5 made up of, forexample, a silicon oxide film are sequentially deposited. After that,the hard mask 5, the upper electrode 4, and the chalcogenide materiallayer 3 are processed by a known lithographic technique and dry etchingtechnique. Then, a sidewall protective film 12 made up of, for example,a silicon nitride film is deposited, and an interlayer insulating film 6is further deposited, as shown in FIG. 11.

Thus, the sidewalls of the chalcogenide material layer that have beenprocessed by dry etching are fully covered with the protective film,preventing sublimation of the chalcogenide material during theinterlayer insulating film forming process.

The desired conditions for forming the sidewall protective film will nowbe described. Chalcogenide material sublimes when exposed to hightemperature, low pressure conditions, as described with reference toFIG. 7. Therefore, the sidewall protective film must be formed under lowtemperature, high pressure conditions, which correspond to the upperleft portion of FIG. 7. Especially, reducing the process temperature iseffective in preventing sublimation of the chalcogenide material.Exemplary conditions are such that the pressure is 0.1 Pa or more andthe temperature is 450° C. or less, although this may vary depending onthe chalcogenide material.

The desired material for the sidewall protective film will now bedescribed. The sidewall protective film is formed by plasma CVD, etc.,since it must be formed at low temperature. If a silicon oxide film isused as the sidewall protective film, the sidewalls of the chalcogenidematerial (layer) are exposed to oxygen activated by the plasma. In thiscase, since chalcogenide material is easily oxidized, a portion of thechalcogenide material (layer) might be oxidized, resulting in degradedcharacteristics. Therefore, a silicon nitride film is preferably used asthe sidewall protective film, since it is “inactive against chalcogenidematerial” (or does not cause an oxidation problem such as that describedabove) and can be formed by CVD, which is a superior technique in termsof step coverage.

It should be noted that Patent Document 2 (listed above), for example,discloses means for forming a protective film on the sidewalls of achalcogenide material (layer) to prevent its sublimation. However, thistechnique is different from the present invention in that an oxide filmis used as the protective film.

Preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings. It should be notedthat in all figures, like numerals are used to denote components havinglike functions to avoid undue repetition.

First Embodiment

A first embodiment of the present invention will be described withreference to FIG. 12. This embodiment provides an example in whichconductive adhesive layers are formed both over and under thechalcogenide material layer.

First of all, a semiconductor substrate 101 is provided, and a MOStransistor is formed on the substrate as a select transistor.Specifically, trench isolation (or device separation) oxide films 102for isolating the MOS transistor are formed in the surface of thesemiconductor substrate 101 by a known selective oxidation technique orshallow trench isolation technique. The present embodiment uses theshallow trench isolation technique, which also can planarize thesurface. First, isolation trenches are formed in the substrate by aknown dry etching technique. Then, after removing damage loft on thesidewalls and bottoms of the trenches in the previous dry etchingprocess, an oxide film is deposited by a known CVD technique. Then,portions of the oxide film other than those in the trenches are polished(and thereby removed) by a known CMP technique, leaving the trenchisolation oxide films 102 within the trenches.

Then, though not shown in the figure, wells of two different conductivetypes are formed by high-energy impurity implantation.

Then, after cleaning the surface of the semiconductor substrate, a gateoxide film 103 (for the MOS transistor) is grown by a known thermaloxidation technique. Then, a gate electrode 104 of polysilicon and asilicon nitride film 105 are (sequentially) deposited on the surface ofthe gate oxide film 103. After that, the gate is processed by alithographic process and a dry etching process, and then impurities areimplanted using the gate electrode and a resist as masks to formdiffusion layers 106. It should be noted that although according to thepresent embodiment the gate electrode is made of polysilicon, it may bea polymetal gate (low resistance gate) having a laminated structure(metal/barrier metal/polysilicon).

Then, a silicon nitride film 107 is deposited by CVD. (This film is usedto help form self-aligned contacts.)

Then, an interlayer insulating film 108 made up of a silicon oxide filmis deposited on the entire surface, and its surface roughness due to thegate electrode is removed by a known CMP technique, planarizing thesurface. After that, plug contact holes are formed by a lithographicprocess and a dry etching process. At that time, to prevent exposure ofthe gate electrode, the interlayer insulating film 108 is processedunder the so-called self-alignment conditions, that is, the interlayerinsulating film 108 (i.e., a silicon oxide film) is selectively etchedagainst the silicon nitride film 107 with a high selectivity ratio.

It should be noted that the following process may be used to ensure thatthe plug contact holes are fully connected with the diffusion layers 106without causing a problem to other layers: first, the interlayerinsulating film (or silicon oxide film) 108 is selectively dry etchedagainst the silicon nitride film with a high selectivity ratio so as toleave the portions of the silicon nitride film on the top surfaces ofthe diffusion layers 106; and then the silicon nitride film isselectively dry etched against the silicon oxide film with a highselectivity ratio to remove the portions of the silicon nitride filmleft on the top surfaces of the diffusion layers 106.

Then, tungsten layers (or tungsten) are formed buried in the plugcontact holes, and tungsten plugs 109 are formed by a known CMPtechnique (that is, the tungsten layers are processed into tungstenplugs 109 by a known CMP technique).

Then, a tungsten layer is newly deposited to a thickness of 100 nm bysputtering and processed by a lithographic process and a dry etchingprocess to form first wiring layers 110A and 110B. After that, aninterlayer insulating film 111 made up of a silicon oxide film isdeposited on the entire surface, and its surface roughness due to thefirst wiring layers is removed by a known CMP technique, planarizing thesurface. Then, a plug contact hole is formed by a lithographic processand a dry etching process and filled with a tungsten layer. Then, atungsten plug 112 is formed by a known CMP technique.

Then, the following layers are sequentially deposited by a knownsputtering technique: a conductive adhesive layer 113 of titanium havinga thickness of 1 nm, a chalcogenide material layer 114 of GeSbTe havinga thickness of 100 nm, a conductive adhesive layer 115 of titaniumhaving a thickness of 1 nm, and an upper electrode 116 of tungstenhaving a thickness of 50 nm. After that, a silicon oxide film 117 isdeposited by a known CVD technique. Then, the silicon oxide film 117,the upper electrode 116, the conductive adhesive layer 115, thechalcogenide material layer 114, and the conductive adhesive layer 113are sequentially processed by a known lithographic process and dryetching process.

It should be noted that the chalcogenide material may be crystallized byheat treatment after depositing the upper electrode 116 or the siliconoxide film 117. This heat treatment process can be performed under anyconditions that allow the chalcogenide material to crystallize.Exemplary conditions are such that the treatment atmosphere is an argongas or nitrogen gas atmosphere; the treatment temperature is 200-600°C.; and the treatment time is 1-10 minutes.

Then, an interlayer insulating film 118 made up of a silicon oxide filmis deposited on the entire surface, and its surface roughness is removedby a known CMP technique, planarizing the surface. After that, a plugcontact hole is formed by a lithographic process and a dry etchingprocess. Then, a tungsten layer is buried in the plug contact hole, anda tungsten plug 119 is formed by a known CMP technique. Then, analuminum layer is deposited to a thickness of 200 nm and processed toform a second wiring layer 120. It should be noted that copper, whichhas lower resistance than aluminum, may be used instead of aluminum.

This substantially completes manufacture of the phase change memory cellof the present embodiment.

According to the present embodiment, adhesive layers are formed over andunder the chalcogenide material layer, which increases the delaminationstrength of the chalcogenide material layer and thereby prevents itsdelamination during the manufacturing process.

Although the above example uses Ti films as the adhesive layers, thepresent embodiment is not limited to this particular material. Theadhesive layers may be conductive films such as Al, Ta, Si, Ti nitride,Al nitride, Ta nitride, W nitride, TiSi, TaSi, WSi, TiW, TiAl nitride,TaSi nitride, TiSi nitride, or WSi nitride films. Further, the adhesivelayers may be formed of a compound of Ti and To or a compound of Al andTe.

It should be noted that the present invention is not limited to thepreferred embodiments described above. It is obvious that the presentinvention embraces all means described in the “Best Modes for Carryingout the Invention” section of this specification.

Second Embodiment

A second embodiment of the present invention will be described withreference to FIG. 13. This embodiment provides an example in which; aconductive adhesive layer is formed at the interface between thechalcogenide material layer and the plug; an insulative adhesive layeris formed at the interface between the chalcogenide material layer andthe interlayer insulating film; and a conductive adhesive layer isformed at the interface between the chalcogenide material layer and theupper electrode.

Since the steps before and including the step of forming the tungstenplug 112 are the same as those described in connection with the firstembodiment, a description of these steps is not provided herein.

There will now be described a process of forming an insulative adhesivelayer 121 and a conductive adhesive layer 122 on the interlayerinsulating film 111 and on the tungsten plus 112, respectively, in aself-aligned manner. First, a titanium layer is deposited on the entiresurfaces of the interlayer insulating film 111 and the tungsten plug 112to a thickness of 3 nm by sputtering and then heat treated. Sincetitanium has a lower free energy of oxide formation than silicon, theportion of the titanium layer deposited on the interlayer insulatingfilm 111 (that is, a silicon oxide film) reacts with oxygen in theunderlying interlayer insulating film 111 to form a titanium oxide film.The portion of the titanium layer deposited on the tungsten plug 112, onthe other hand, reacts with tungsten in the underlying tungsten plug 112to form a conductive titanium-tungsten alloy. Thus, the insulativeadhesive layer 121 is formed on the interlayer insulating film 111 andthe conductive adhesive layer 122 is formed on the tungsten plug 112 ina self-aligned manner.

The above heat treatment can be performed at any temperature that causestitanium to react with the silicon oxide film. However, 400° C. or ahigher temperature is preferred to form a favorable titanium oxide film.Further, the heat treatment is preferably performed in an inertatmosphere to prevent oxidation of the conductive adhesive layer.Exemplary conditions are such that the treatment atmosphere is an argongas atmosphere; the treatment temperature is 400-800° C.; and thetreatment time is 1-10 minutes.

Then, a chalcogenide material layer 114 of GeSbTe having a thickness of100 nm, a conductive adhesive layer 115 of titanium having a thicknessof 1 nm, and an upper electrode 116 of tungsten having a thickness 50 nmare sequentially deposited by a known sputtering technique. After that,a silicon oxide film 117 is deposited by a known CVD technique. Then,the silicon oxide film 117, the upper electrode 116, the conductiveadhesive layer 115, the chalcogenide material layer 114, and theinsulative adhesive layer 121 are sequentially processed by a knownlithographic process and dry etching process.

It should be noted that the chalcogenide material may be crystallized byheat treatment after depositing the upper electrode 116 or the siliconoxide film 117. This heat treatment process can be performed under anyconditions that allow the chalcogenide material to crystallize.Exemplary conditions are such that: the treatment atmosphere is an argongas or nitrogen gas atmosphere; the treatment temperature is 200-600°C.; and the treatment time is 1-10 minutes.Since the steps following the above step are the same as those describedin connection with the first embodiment, a description thereof is notprovided herein.

These steps substantially complete manufacture of the phase changememory cell of the present embodiment.

According to the present embodiment, adhesive layers are formed over andunder the chalcogenide material layer, which increases the delaminationstrength of the chalcogenide material layer and thereby prevents itsdelamination during the manufacturing process. Further, since aconductive adhesive layer is formed at the interface between thechalcogenide material layer and the plug, a current can be efficientlydelivered to the chalcogenide material. Still further, since aninsulative or nonconductive) adhesive layer is formed at the interfacebetween the chalcogenide material layer and the interlayer insulatingfilm, the current required to reprogram the chalcogenide material (orthe memory cell) can be reduced.

Although in the above example the adhesive layers formed on theinterlayer in film and the plug are formed of Ti, the present embodimentis not limited to this particular material. Any metal having a lowerfree energy of oxide formation than Si, such as Zr, Hf, or Al, can beused, with the same effect.

It should be noted that the present invention is not limited to thepreferred embodiments described above. It is obvious that the presentinvention embraces all means described in the “Best Modes for Carryingout the Invention” section of this specification.

Third Embodiment

A third embodiment of the present invention will be described withreference to FIG. 14. This embodiment provides an example in which aprotective film is formed on the sidewalls of the chalcogenide materiallayer.

Since the steps before and including the step of forming the tungstenplug 112 are the same as those described in connection with the firstembodiment, a description of these steps is not provided herein.

First, a chalcogenide material layer 114 of GeSbTe having a thickness of100 nm and an upper electrode 116 of tungsten having a thickness of 50nm are sequentially deposited over the entire surfaces of the interlayerinsulating film 111 and the tungsten plug 112 by a known sputteringtechnique. After that, a silicon oxide film 117 is deposited by a knownCVD technique. Then, the silicon oxide film 117, the upper electrode116, and the chalcogenide material layer 114 are sequentially processedby a known lithographic process and dry etching process. It should benoted that the chalcogenide material may be crystallized by heattreatment after depositing the upper electrode 116 or the silicon oxidefilm 117. This heat treatment process can be performed under anyconditions that allow the chalcogenide material to crystallize.Exemplary conditions are such that: the treatment atmosphere is an argongas or nitrogen gas atmosphere; the treatment temperature is 200-600°C.; and the treatment time is 1-10 minutes.

Then, a sidewall protective film 123 made up of a silicon nitride filmis deposited to a thickness of 20 nm by a known CVD technique. It shouldbe noted that this sidewall protective film must be formed under hightemperature, low pressure conditions to prevent sublimation of thechalcogenide material. Exemplary conditions are such that the pressureis 0.1 Pa or more and the temperature is 450° C. or less.

Then, an interlayer insulating film 118 made up of a silicon oxide filmis deposited on the entire surface, and its surface roughness is removedby a known CMP technique, planarizing the surface. After that, a plugcontact hole is formed by a lithographic process and a dry etchingprocess. Then, a tungsten layer is formed buried in the plug contacthole, and a tungsten plug 119 is formed by a known CMP technique. Then,an aluminum layer is deposited to a thickness of 200 nm and processed toform a second wiring layer 120. (It should be noted that copper, whichhas lower resistance than aluminum, may be used instead of aluminum.)

This substantially completes manufacture of the phase change memory cellof the present embodiment. According to the present embodiment, thesidewalls of the chalcogenide material layer that have been processed bydry etching are fully covered with a protective film, preventingsublimation of the chalcogenide material during the interlayerinsulating film forming process.

The above example uses a silicon nitride film as the sidewall protectivefilm. The reason for this is that if a silicon oxide film is used as thesidewall protective film, the sidewalls of the chalcogenide material(layer) might be oxidized, resulting in degraded characteristics. Inaddition, the silicon nitride film helps process regions other than thechalcogenide material layer 114 region in a self-aligned manner.Such a process will be described with reference to FIG. 15. FIG. 15shows a structure to the left of the structure shown in FIG. 12, 13, or14. Referring to FIG. 15, a first wiring layer 110B is electricallyconnected to the source or drain of the MOS transistor (shown in FIGS.12 to 14).

Since the steps before and including the step of depositing the siliconnitride film 123 to a thickness of 20 nm by a known CVD technique arethe same as those described in connection with the third embodiment, adescription of these steps is not provided herein. Note that the siliconnitride film 123 shown in FIG. 15 corresponds to the sidewall protectivefilm 123 (for the chalcogenide material layer) shown in FIG. 14. Then,an interlayer insulating film 118 made up of a silicon oxide film isdeposited on the entire surface, and its surface roughness is removed bya known CMP technique, planarizing the surface. After that, a plugcontact hole reaching the surface of the silicon nitride film 123 isformed by a lithographic process and a dry etching process. This dryetching process is performed under such conditions that the etching rateof the silicon oxide film is higher than that of the silicon nitridefilm. Then, dry etching is further performed under such conditions thatthe etching rate of the silicon nitride film is higher than that of thesilicon oxide film to extend the plug contact hole to the surfaces ofthe tungsten plug 112 and the interlayer insulating film 111.

In the above process, even if the plug contact hole is misaligned withthe tungsten plug 112, the interlayer insulating film 111 is not deeplyetched.

Then, a tungsten layer is formed buried in the plug contact hole, and atungsten plug 119 is formed by a known CMP technique. After that, analuminum layer is deposited to a thickness of 200 nm and processed toform a second wiring layer 120. It should be noted that copper, whichhas lower resistance than aluminum, may be used instead of aluminum.

Thus, this process allows the tungsten plug 119 to be formed on thetungsten plug 112 in a self-aligned manner. Therefore, a silicon nitridefilm is preferably used as the sidewall protective film for thechalcogenide material layer.

It should be noted that the present invention is not limited to thepreferred embodiments described above. It is obvious that the presentinvention embraces all means described in the “Best Modes for Carryingout the Invention” section of this specification.

Although the present invention has been specifically described based onpreferred embodiments thereof, it should be understood that theinvention is not limited to these embodiments and various alterationsmay be made thereto without departing from the scope and spirit of theinvention.

As described above, the first and second embodiments provide exemplaryadhesive layers and the third embodiment provides an exemplary sidewallprotective film, separately. However, these embodiments may be combinedas necessary to collectively utilize their effects.

There will now be described technical ideas of the present inventionother than those indicated by the appended claims. (These technicalideas can be understood from the above description of the preferredembodiments.)

1) A method for manufacturing a semiconductor integrated circuit device,comprising the steps of:

forming a select transistor in a memory cell region on a semiconductorsubstrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a conductive adhesive layer on the second plug, forming a phasechange material layer, another conductive adhesive layer, and an upperelectrode laminated to one another so as to cover the conductiveadhesive layer, and forming an insulative (or nonconductive) adhesivelayer between the first interlayer insulating film and the phase changematerial layer;

forming a silicon nitride film so as to cover the multilayer film;

forming a second interlayer insulating film over the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

2) A method for manufacturing a semiconductor integrated circuit device,comprising the steps of:

forming a select transistor in a memory cell region on a semiconductorsubstrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a multilayer film on the first interlayer insulating film, themultilayer film including a first adhesive layer, a phase changematerial layer, a second adhesive layer, and an upper electrodelaminated to one another, the first adhesive layer being connected tothe second plug;

forming a silicon nitride film so as to cover the multilayer film;

forming a second interlayer insulating film over the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

3) A method for manufacturing a semiconductor integrated circuit device,comprising the steps of:

forming a select transistor in a memory cell region on a semiconductorsubstrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a multilayer film on the first interlayer insulating film, themultilayer film including a first adhesive layer, a phase changematerial layer, a second adhesive layer, and an upper electrodelaminated to one another, the first adhesive layer being connected tothe second plug;

forming a second interlayer insulating film on the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

4) A method for manufacturing a semiconductor integrated circuit device,comprising the steps of:

forming a select transistor in a memory cell region on a semiconductorsubstrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a multilayer film on the first interlayer insulating film, themultilayer film including a first adhesive layer, a phase changematerial layer, and an upper electrode laminated to one another, thefirst adhesive layer being connected to the second plug;

forming a second interlayer insulating film on the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

5) A method for manufacturing a semiconductor integrated circuit device,comprising the steps of forming a select transistor in a memory cellregion on a semiconductor substrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a multilayer film on the first interlayer insulating film, themultilayer film including a phase change material layer and a secondadhesive layer, and an upper electrode laminated to one another, thephase change material layer being connected to the second plug;

forming a second interlayer insulating film on the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

6) The method described in item 1 or 2 above, wherein:

the silicon nitride film is formed to extend into the peripheralcircuitry region;

the fifth-plug forming step includes a step of forming a via for thefifth plug in the second interlayer insulating film; and

the silicon nitride film is used as an etching stopper at the viaforming step.

7) A method for manufacturing a semiconductor integrated circuit device,comprising the steps of:

forming a select transistor in a memory cell region on a semiconductorsubstrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a multilayer film on the first interlayer insulating film, themultilayer film including a conductive adhesive layer, a phase changematerial layer, and an upper electrode laminated to one another, theconductive adhesive layer being connected to the second plug;

forming a second interlayer insulating film on the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

8) A method for manufacturing a semiconductor integrated circuit device,comprising the steps of forming a select transistor in a memory cellregion on a semiconductor substrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a phase change material layer and an upper electrode laminatedover the second plug, and forming an insulative adhesive layer betweenthe first interlayer insulating film and the phase change materiallayer:

forming a second interlayer insulating film on the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

9) A method for manufacturing a semiconductor integrated circuit device,comprising the steps of:

forming a select transistor in a memory cell region on a semiconductorsubstrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a conductive adhesive layer on the second plug, and forming aphase change material layer, another conductive adhesive layer, and anupper electrode laminated to one another so as to cover the conductiveadhesive layer;

forming a second interlayer insulating film on the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

10) A method for manufacturing a semiconductor integrated circuitdevice, comprising the steps of:

forming a select transistor in a memory cell region on a semiconductorsubstrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a conductive adhesive layer on the second plug, forming a phasechange material, another conductive adhesive layer, and an upperelectrode laminated to one another so as to cover the conductiveadhesive layer, and forming an insulative adhesive layer between thefirst interlayer insulating film and the phase change material layer;

forming a second interlayer insulating film on the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

11) A method for manufacturing a semiconductor integrated circuitdevice, comprising the steps of:

forming a select transistor in a memory cell region on a semiconductorsubstrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a multilayer film on the second plug, the multilayer filmincluding a phase change material layer, a conductive adhesive layer,and an upper electrode laminated to one another;

forming a second interlayer insulating film on the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

12) A method for manufacturing a semiconductor integrated circuitdevice, comprising the steps of:

forming a select transistor in a memory cell region on a semiconductorsubstrate and forming peripheral circuitry;

forming first plugs connected to the select transistor;

forming first wires in the memory cell region and in the peripheralcircuitry region;

forming a first interlayer insulating film on the first wires;

forming a second plug and a third plug in the first interlayerinsulating film, the second and third plugs being connected to the firstwires formed in the memory cell region and in the peripheral circuitryregion, respectively;

forming a multilayer film on the second plug, the multilayer filmincluding a phase change material layer and an upper electrode laminatedto each other;

forming a silicon nitride film so as to cover the multilayer film;

forming a second interlayer insulating film over the upper electrode;

forming a second wire on the second interlayer insulating film;

forming a fourth plug connected between the upper electrode and thesecond wire; and

forming a fifth plug in the second interlayer insulating film, the fifthplug being connected to the third plug.

INDUSTRIAL APPLICABILITY

The present invention can be applied to semiconductor integrated circuitdevices that employ phase change memory cells formed of a phase changematerial such as chalcogenide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a phase change memory cell accordingto the present invention.

FIG. 2 is a diagram showing specifications of current pulses forchanging the phase state of chalcogenide.

FIG. 3 is a cross-sectional view showing a step in a process ofmanufacturing a phase change memory cell using a conventional technique.

FIG. 4 is a cross-sectional view showing another step in the process ofmanufacturing a phase change memory cell using a conventional technique.

FIG. 5 is a cross-sectional view showing still another step in theprocess of manufacturing a phase change memory cell using a conventionaltechnique.

FIG. 6A is a diagram showing results of thermal desorption spectrometryof a GeSbTe film.

FIG. 6B is a diagram showing results of thermal desorption spectrometryof a GeSbTe film.

FIG. 6C is a diagram showing results of thermal desorption spectrometryof a GeSbTe film.

FIG. 7 is a graph showing the sublimation characteristics of a GeSbTefilm, wherein the horizontal axis represents temperature and thevertical axis represents pressure.

FIG. 8 is a diagram comparing critical delamination load measurementresults obtained from scratch tests.

FIG. 9A is a diagram illustrating how an adhesive layer affects thetemperature vs. resistance characteristics of a GeSbTe film.

FIG. 9B is another diagram illustrating how an adhesive layer affectsthe temperature vs. resistance characteristics of a GeSbTe film.

FIG. 10 is a cross-sectional view of a phase change memory cell of thepresent invention.

FIG. 11 is a cross-sectional view of another phase change memory cell ofthe present invention.

FIG. 12 is a cross-sectional view of a phase change memory cellaccording to a first embodiment of the present invention.

FIG. 13 is a cross-sectional view of a phase change memory cellaccording to a second embodiment of the present invention.

FIG. 14 is a cross-sectional view of a phase change memory cellaccording to a third embodiment of the present invention.

FIG. 15 is another cross-sectional view of the phase change memory cellaccording to the third embodiment.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 . . . interlayer insulating film    -   2 . . . plug    -   3 . . . chalcogenide material layer    -   4 . . . upper electrode    -   5 . . . hard mask    -   6 . . . interlayer insulating film    -   7 . . . adhesive layer    -   8 . . . adhesive layer    -   9 . . . conductive adhesive layer    -   10 . . . insulative adhesive layer    -   11 . . . conductive adhesive layer    -   12 . . . sidewall protective film    -   101 . . . semiconductor substrate    -   102 . . . trench isolation oxide film    -   103 . . . gate oxide film    -   104 . . . gate electrode    -   105 . . . silicon nitride film    -   106 . . . diffusion layer    -   107 . . . silicon nitride film    -   108 . . . interlayer insulating film    -   109 . . . tungsten plug    -   110A, 110B . . . first wiring layer    -   111 . . . interlayer insulating film    -   112 . . . tungsten plug    -   113 . . . conductive adhesive layer    -   114 . . . chalcogenide material layer    -   115 . . . conductive adhesive layer    -   116 . . . upper electrode    -   117 . . . silicon oxide film    -   118 . . . interlayer insulating film    -   119 . . . tungsten plug    -   120 . . . second wiring layer    -   121 . . . insulative adhesive layer    -   122 . . . conductive adhesive layer    -   123 . . . sidewall protective film (silicon nitride film)

1. A semiconductor memory device comprising: a semiconductor substrate;a select transistor formed on a principal surface of said semiconductorsubstrate; an interlayer insulating film provided on said selecttransistor; a plug provided so as to penetrate through said interlayerinsulating film, said plug being electrically connected to said selecttransistor; a phase change material layer provided on said interlayerinsulating film such that a portion of said phase change material layeris connected with said plug; an upper electrode provided on said phasechange material layer; and an adhesive layer provided between an undersurface of said phase change material layer and a top surface of saidinterlayer insulating film and between said under surface of said phasechange material layer and a top of said plug. 2-23. (canceled)